1. Field of the Invention
The invention relates to an interconnection (contact) element suitable for effective pressure connections between electronic components.
2. Description of Related Art
Interconnection or contact elements may be used to connect devices of an electronic component or one electronic component to another electronic component. For example, a contact element may be used to connect two circuits of an integrated circuit chip or including an application specific integrated circuit (ASIC). Contact elements may also be used to connect the integrated circuit chip to a chip package suitable for mounting on a printed circuit board of a computer or other electronic device. Contact elements may further be used to connect the integrated circuit chip to a test device such as a probe card assembly or other printed circuit board (PCB) to test the chip.
Generally, interconnection or contact elements between electronic components can be classified into at least the two broad categories of "relatively permanent" and "readily demountable."
An example of a "relatively permanent" contact element is a wire bond. Once two electronic components are connected to one another by a bonding of a contact element to each electronic component, a process of unbending must be used to separate the components. A wire bond contact element, such as between an integrated circuit chip or die and inner leads of a chip or package (or inner ends of lead frame fingers) typically utilizes a "relatively permanent" contact element.
One example of a "readily demountable" contact element is the contact element between rigid pins of one electronic component received by resilient socket elements of another electronic component. A second type of a "readily demountable" contact element is a contact element that itself is resilient or spring-like or mounted in or on a spring or resilient medium. An example of a contact element is a tungsten needle of a probe card component. The contact element of a probe card component is typically intended to effect a temporary pressure connection between an electronic component to which the spring contact element is mounted and terminals of a second electronic component, such as a semiconductor device under test.
With regard to spring contact elements, generally, a certain minimum contact force is desired to effect reliable pressure contact to an electronic component (e.g., to terminals on electronic component). For example, a contact (load) force of approximately 15 grams (including as little as 2 grams or less and as much as 150 grams or more, per terminal) may be desired to effect a reliable electrical pressure connection to a terminal of an electronic component.
A second factor of interest with regard to spring contact elements is the shape and metallurgy of the portion of the spring contact element making pressure connection to the terminal of the electronic component. With respect to the tungsten needle as a spring contact element, for example, the contact end is limited by the metallurgy of the interconnection element (i.e., tungsten) and, as the tungsten needle becomes smaller in diameter, it becomes commensurately more difficult to control or establish a desired shape at the contact end.
In certain instances, spring contact elements themselves are not resilient, but rather are supported by a resilient membrane. Membrane probes exemplify this situation, where a plurality of microbumps are disposed on a resilient membrane. Again, the technology required to manufacture such contact elements limits the design choices for the shape and metallurgy of the contact portion of the contact elements.
Commonly-owned U.S. patent application Ser. No. 08/152,812 filed Nov. 16, 1993 (now U.S. Pat. No. 4,576,211, issued Dec. 19, 1995), and its counterpart commonly-owned co-pending "divisional" U.S. patent application Ser. Nos. 08/457,479 filed Jun. 1, 1995 (status: pending) and 08/570,230 filed Dec. 11, 1995 (status: pending), all by Khandros, disclose methods for making spring contact elements. In a preferred embodiment, these spring contact elements, which are particularly useful for micro-electronic applications, involve mounting an end of a flexible elongate core element (e.g., wire "stem" or "skeleton") to a terminal on an electronic component, coating the flexible core element and adjacent surface of the terminal with a "shell" of one or more materials. One of skill in the art can select a combination of thickness, yield strength, and elastic modulus of the core and shell materials to provide satisfactory force-to-deflection characteristics of the resulting spring contact elements. Exemplary materials for the core element include gold. Exemplary materials for the coating include nickel and its alloys. The resulting spring contact element is suitably used to effect pressure, or demountable, interconnections between two or more electronic components, including semiconductor devices.
Commonly-owned, co-pending U.S. patent application Ser. No. 08/340,144 filed Nov. 15, 1994 and its corresponding PCT U.S. patent application Ser. No. PCT/US94/13373 filed Nov. 16, 1994 (WO95/14314, published May 16, 1995), both by Khandros and Mathieu, disclose a number of applications for the aforementioned spring contact elements, and also disclose techniques for fabricating contact pads at the ends of the spring contact elements. For example, a plurality of negative projections or holes, which may be in the form of inverted pyramids ending in apexes, are formed in the surface of a sacrificial layer (substrate). These holes are then filled with a contact structure comprising layers of material such as gold or rhodium and nickel. A flexible elongate element is mounted to the resulting contact element structure and can be overcoated in the manner described hereinabove. In a final step, the sacrificial substrate is removed. The resulting spring contact element has a contact pad having controlled geometry (e.g., a sharp point) at its free end.
Commonly-owned, co-pending U.S. patent application Ser. No. 08/452,255 filed May 26, 1995 and its corresponding PCT U.S. patent application Ser. No. PCT/US95/14909 filed Nov. 13, 1995 (WO96/17278, published Jun. 6, 1996), both by Eldridge, Grube, Khandros and Mathieu, disclose additional techniques and metallurgies for fabricating contact tip structures on sacrificial substrates, as well as techniques for transferring a plurality of spring contact elements mounted thereto, en masse, to terminals of an electronic component.
Commonly-owned, co-pending U.S. Provisional Patent Application No. 60/005,189 filed May 17, 1996 and its corresponding PCT Patent Application Ser. No. PCT/US96/08107 filed May 24, 1996 (WO96/37332, published Nov. 28, 1996), both by Eldridge, Khandros and Mathieu, disclose techniques whereby a plurality of contact tip structures are joined to a corresponding plurality of elongate contact elements that are already mounted to an electronic component. Also disclosed are techniques for fabricating "elongate" contact tip structures in the form of cantilevers. The cantilever tip structures can be tapered, between one end thereof and an opposite end thereof. The cantilever tip structures are suitable for mounting to already-existing (i.e., previously fabricated) raised contact elements extending (e.g., free-standing) from corresponding terminals of an electronic component.
Commonly-owned, co-pending U.S. patent application Ser. No. 60/024,555 filed Aug. 26, 1996, by Eldridge, Khandros and Mathieu, representatively discloses a technique whereby a plurality of elongate tip structures having different lengths than one another can be arranged so that their outer ends are disposed at a greater pitch than their inner ends. The inner, "contact" ends may be collinear with one another, for effecting connections to electronic components having terminals disposed along a line, such as a center line of the component.
As electronic components get increasingly smaller and the spacing between terminals on the electronic components get increasingly tighter or the pitch gets increasingly finer, it becomes increasingly more difficult to fabricate interconnections including spring contact elements suitable for making electrical connection to terminals of an electronic component. Co-pending and commonly-owned U.S. patent application Ser. No. 08/802,054, titled "Microelectronic Contact Structure, and Method of Making Same," discloses a method of making spring contact elements through lithographic techniques. In one embodiment, that application discloses forming a spring contact element (including a spring contact element that is a cantilever beam) on a sacrificial substrate and then transferring and mounting the contact element to a terminal on an electronic component. In that disclosure, the spring contact element is formed in the substrate itself through etching techniques. In co-pending, commonly-owned U.S. patent application, Ser. No. 08/852,152, titled "Microelectronic Spring Contact Elements," spring contact elements are formed on a substrate, including a substrate that is an electronic component, by depositing and patterning a plurality of masking layers to form an opening corresponding to a shape embodied for the spring contact element, depositing conductive material in the opening made by the patterned masking layers, and removing the masking layer to form the free-standing spring contact element.
Co-pending and commonly-owned U.S. patent application, Ser. No. 09/023,859, titled "Microelectronic Contact Structures and Methods of Making Same," describes a contact element having a base end portion (post component), a middle portion (beam component) and a contact end portion (tip component) and methods separately forming each portion and joining the post portion together as desired on an electronic component.
What is needed is a method of fabricating interconnections suitable for present fine-pitch electrical connections that is scalable for future technologies. Also needed are improved methods of making contact elements particularly methods that are repeatable, consistent, and inexpensive.